Efficient active multi-drive radiator

ABSTRACT

An integrated Multi-Port Driven (MPD) antenna that can be driven at many points with different signals. An integrated MPD radiating source utilizing an 8-phase ring oscillator and eight power amplifiers to drive the MPD antenna at 161 GHz with a total radiated power of −2 dBm and a single element EIRP of 4.6 dBm has been demonstrated in silicon with single lobe well behaved radiation patterns closely matching simulation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of co-pending U.S.provisional patent application Ser. No. 61/548,665 filed Oct. 18, 2011,which application is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY FUNDED RESEARCH OR DEVELOPMENT

This invention was made with government support under FA8650-09-C-7924awarded by USAF/ESC. The government has certain rights in the invention.

FIELD OF THE INVENTION

The invention relates to antennas or radiators in general andparticularly to an on-chip antenna or radiator.

BACKGROUND OF THE INVENTION

Wireless communication continues to increase in popularity, driving upthe demand for wireless bandwidth. This has caused the spectrum at lowerfrequencies to become crowded. The need to be able to utilize additionalspectrum at higher millimeter-wave frequencies has become critical. Atthe same time, the maximum operating frequencies of transistors, fmax,for example CMOS devices, have increased through transistor scaling tothe point where it is feasable to integrate an entire transmitter systemon a chip. However, there are several obsticles to overcome usingtechnologies such as CMOS at these frequencies. In addition, because anefficient antenna must be at least around λ/2 in dimension, traditionalantennas were fabricated off chip, and connected to the rest of thetransmitter through a printed circuit board (pcb) or cable.

Traditional RF circuit design divides all circuit functionality intoblocks, representing baseband circuitry, mixers, oscillators, phaserotators, amplifiers and antennas. Each block is designed separately,and the blocks are connected, often through only one connection, whichcan be either a single ended connection or a differential connection.Because the antenna is commonly fabricated off chip, and requires anexternal connection, most antennas have a single drive point, requiringa single output from the power amplifier.

However, integrated power generation and particularly radiation presentseveral challenges ranging from on-chip power combining and impedancematching to off-chip power transfer. The traditional power transfermethods (e.g., bonding wires and solder balls or solder bumps) tooff-chip loads (e.g., external antenna) also become increasinglyineffective.

At the same time, the smaller wavelengths associated with thesefrequencies opens up the possibility of radiating the power directlyfrom the chip itself, rather than losing significant power byelectrically connecting to an off-chip antenna. The low breakdownvoltages of integrated silicon transistors encourages the use of largetransistors or highly parallel transistors for high power generation,leading to low optimal load impedances from the active driver'sperspective. Unfortunately, this directly conflicts with single-portantenna impedance level trade-offs, where a large radiation resistancecompared to the loss resistance is preferred for high efficiency.

Among the disadvantages of the traditional approach at these frequenciesare the losses incurred in transmission lines and interconnects and thelow gain available in amplifier stages. Impedance matching networks onchip often can induce several dB of loss, and efficient inteconnects toan off chip-board or cable are not feasable or rugged enough for massproduction. A design approach is needed that can remove as muchunnessisary loss in the transmitter chain as possible.

There is a need for improved systems and methods that permit integratedchips to efficiently and effectively radiate power in the millimeterwave regime.

SUMMARY OF THE INVENTION

According to one aspect, the invention features a multi-port drivenantenna. The multi-port driven antenna, comprises an antenna structurehaving a length L, the antenna structure comprising a conductor andconfigured to radiate electromagnetic radiation, the radiator structurehaving at least one ground contact point and a plurality S of inputports, where S is a positive integer greater than or equal to 2, each ofthe plurality S of input ports having a respective electrical connectionto the antenna at a respective selected location along the antennalength L; and a respective signal input terminal of each of theplurality S of input ports, each signal input terminal configured toreceive a respective input signal having a predetermined phaserelationship with respect to another input signal applied an adjacentsignal input terminal, the predetermined phase relationship dependent onthe location of the respective electrical connection to the antenna, therespective signal input terminal configured to apply the receivedrespective signal to the antenna structure at the respective selectedlocation of the input port.

In one embodiment, the multi-port driven antenna further comprises asource of input signals, the source configured to provide to each of therespective signal input terminal of each of the plurality S of inputports the respective input signal having a predetermined phaserelationship with respect to another input signal applied an adjacentsignal input terminal, and configured to provide a ground signal at eachof the at least one ground contact point; the multi-port driven antennaand the source of input signals when active defining a multiport-drivenradiator.

In another embodiment, the source of input signals includes an amplifierconfigured to amplify at least one of the respective input signals.

In yet another embodiment, the antenna structure having a length L is aloop structure.

In still another embodiment, each of the plurality S of input ports hasa respective electrical connection separated by a length L/S from alocation of an adjacent input port.

In a further embodiment, the signal source is a multi-phase oscillator.

In yet a further embodiment, the multi-phase oscillator is configured toprovide 2^(X) phases, where X is an integer greater than or equal to 2.

In an additional embodiment, the antenna is configured to radiatemillimeter wave electromagnetic radiation.

In one more embodiment, the multi-port driven antenna is fabricated on asemiconductor wafer.

In still a further embodiment, the multi-port driven antenna furthercomprises at least one ground plane adjacent the loop antenna structure.

In a further embodiment, the multi-port driven antenna further comprisesa controller configured to control an amplitude and a phase of each ofthe respective input signals.

In yet a further embodiment, the multi-port driven antenna furthercomprises a controller configured to control a power supply.

In an additional embodiment, the multi-port driven antenna is configuredas one of a plurality of multi-port driven antennas in a phased arrayconfiguration.

In one more embodiment, the antenna structure having a length L is alinear structure.

According to another aspect, the invention relates to a method ofgenerating electromagnetic radiation. The method comprises the steps of:providing an antenna comprising: an antenna structure having a length L,the antenna structure comprising a conductor and configured to radiateelectromagnetic radiation, the radiator structure having at least oneground contact point and a plurality S of input ports, where S is apositive integer greater than or equal to 2, each of the plurality S ofinput ports having a respective electrical connection to the antenna ata respective selected location along the antenna length L; and arespective signal input terminal of each of the plurality S of inputports, each signal input terminal configured to receive a respectiveinput signal having a predetermined phase relationship with respect toanother input signal applied an adjacent signal input terminal, thepredetermined phase relationship dependent on the location of therespective electrical connection to the antenna, the respective signalinput terminal configured to apply the received respective signal to theantenna structure at the respective selected location of the input port;applying each of a plurality S of input signals each having a frequencyω to a respective signal input terminal of each of the plurality S ofinput ports; and observing an electromagnetic radiation output signal ata frequency ω.

In one embodiment, the integer S is three or larger.

In another embodiment, the integer S is a power of 2.

In yet another embodiment, the integer S is 8.

In still another embodiment, the electromagnetic radiation is millimeterwave electromagnetic radiation.

The foregoing and other objects, aspects, features, and advantages ofthe invention will become more apparent from the following descriptionand from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the invention can be better understood withreference to the drawings described below, and the claims. The drawingsare not necessarily to scale, emphasis instead generally being placedupon illustrating the principles of the invention. In the drawings, likenumerals are used to indicate like parts throughout the various views.

FIG. 1 is a schematic diagram of an active multi-drive radiatoraccording to principles of the invention.

FIG. 2 is a three dimensional plot of radiation intensity as a functionof direction for the embodiment of FIG. 1.

FIG. 3 is a schematic diagram of a linear device, a linear multi-portdriven radiator, according to principles of the invention deposited on asilicon substrate.

FIG. 4 is a plot of current density in the device of FIG. 3.

FIG. 5 is a three dimensional plot of the radiation gain patternachieved by the device shown in FIG. 3 after tuning of the substrate.

FIG. 6 is a three dimensional plot of gain as a function of variationsin the x, y, and z dimensions of the device of FIG. 3.

FIG. 7 is a graph of gain as a function of substrate thickness (Zsub).

FIG. 8 is a schematic diagram of an embodiment of a differential radialmulti-port driven radiator, with a loop topology.

FIG. 9 is a plot of the current density in the multi-port drivenradiator of FIG. 8 at 0° phase.

FIG. 10 is a plot of the current density in the multi-port drivenradiator of FIG. 8 at 90° phase.

FIG. 11 is a schematic diagram of a second embodiment of a differentialradial multi-port driven radiator in a loop topology.

FIG. 12 is a three dimensional plot of the radiation pattern emitted bya differential radial multi-port driven radiator with a loop topology.

FIG. 13A is a schematic block diagram of an embodiment of a single-endedradial multi-port driven (MPD) radiating source having 8 drive spokes ina periodic structure.

FIG. 13B is a schematic block diagram of an embodiment of a single-endedradial multi-port driven (MPD) radiating source having 4 drive spokes ina non-periodic structure.

FIG. 14 is a schematic diagram of the instantaneous current distributionon antenna signal and ground paths at 0° phase.

FIG. 15 is a schematic circuit diagram of an 8-phase ring oscillator andpower mixer, in which the bias circuitry is omitted for simplicity.

FIG. 16 is a circuit diagram of a power amplifier.

FIG. 17 is a graph of a calibrated measured spectrum.

FIG. 18A is a plot of the simulated and measured antenna patterns in theelevation plane.

FIG. 18B is a plot of the simulated and measured antenna patterns in theazimuth plane.

FIG. 19 is an image of a die containing an embodiment of thesingle-ended radial MPD radiating source.

DETAILED DESCRIPTION

The ability to implement complex structures on silicon chips combinedwith the high frequency capabilities of the transistors widens theavailable design space considerably. This enables an integratedMulti-Port Driven (MPD) antenna that can be driven at many points withdifferent signals. As used in this document, the term “MPD antenna” isused to denote a passive conductor apparatus by itself An MPD antenna ascontemplated herein is a conductor, in a linear structure or a loopstructure, having multiple input ports or input terminals, each of whichis intended to be driven at the same time as the others, such that, ifone input port were to become inactive or be disconnected, the MPDantenna would remain active, but might not behave as intended. As usedherein, the term “loop” or “loop structure” denotes a conductor that isformed in a closed path, without regard to the exact shape of the path(e.g., the shape can be circular, polygonal, or any other closed form asmay be convenient). In an MPD antenna, superposition of the signalsprovided by multiple driving sources takes place. By comparison, aphased array of antennas is a structure that comprises a plurality ofindividual antennas, each of which is driven at a single input terminal,such that, if the input to one of the input terminals were to becomeinactive or be disconnected, the antenna driven at that one inputterminal would become inactive, but the other antennas would remainactive. In each of the antennas in phased array, there is nosuperposition of signals from multiple sources.

Such MPD antennas can be used to overturn, or decouple, the trade-offsbetween the port impedance and antenna efficiency due to energy lossesin the antenna. With careful design, taking advantage of the currentsuperposition of many driving sources, low input impedance can beachieved directly at the antenna port while keeping the radiationefficiency high. An added advantage of the MPD structure is itsintrinsic power combing capability, where local current combiningresults in far field power combing. This is particularly conducive tosilicon integrated power generation. Thus, an MPD antenna provides anefficient way to transfer and radiate power off chip, while concurrentlyperforming impedance matching and power combining.

A multi-port driven (MPD) antenna allows for the removal of RF blocksfor impedance matching, power combining, and power delivery by enablingefficient radiation from several output stages driving the antenna. Asused in this document, the term “MPD radiator” is used to denote an MPDantenna that is combined with driving circuitry. A theory of operationof such a MPD radiator is presented. One embodiment of a MPD radiatingsource utilizing an 8-phase ring oscillator and eight power amplifiersto drive the MPD antenna at 161 GHz with a total radiated power of −2dBm and a single element EIRP of 4.6 dBm has been demonstrated insilicon with single lobe well behaved radiation patterns closelymatching simulation.

While this invention is not limited to any given frequency range, it ispresented in one embodiment as operating at millimeter-wave frequencies.In some embodiments, the antenna can be fabricated using on-chip metalsas the conductor structure in the same processes as are used infabricating integrated circuits. In other embodiments, other conductivematerials can be used as the conductor in the antenna structure. Theconventional assumption that the ampifying stages must connect to theantenna through a single connection is no longer valid if one canprovide a sufficient level of integration on a chip, which takesadvantage of the effectively “free” availability of (or extremely lowcost of) transistors on chip. The many potential applications atmillimeter-wave (mm-wave) frequencies combined with our ability tointegrate a large number of high-speed transistors presents anopportunity to construct novel power generation and radiationarchitectures in silicon based integrated circuits. In such a regime,new designs of both amplifiers and antennas are possible. These newintegrated transmitter-antennas are active radiators. What sets anactive radiator apart from a traditional transmitter and antenna is thelevel of integration of the amplifiing transistors into the radiatingstructure itself.

A design approach is provided that can remove as much unnessisary lossin the transmitter chain as possible. In this approach, the blocksadvantageously are all designed from a holistic point of view, ratherthan as individual blocks with 50 Ω connections. The focus of thisinvention is the combination of the driving circuitry and antenna intoone radiating structure including, in some embodiments, even the entireoscillator amplifier chain with the radiator.

Several different types of MPD radiators are described herein.

In one embodiment (First Embodiment), a loop MPD radiator has multipleinput terminals spaced apart along the loop, all of which inputterminals are driven with differential feeds, all of which have the samephase. An example of such a radiator is illustrated in FIG. 1.

In still another embodiment, a design termed a differential radial MPDradiator has a loop conductor with a plurality S of differential feedswhich span a phase space of 2Nπ, where N is an integer, and each feedhas a phase shift of 2πN/S compared to each of the two adjacent feeds.Embodiments of this type of MPD radiator are shown in FIG. 8 and FIG.11. The First Embodiment described above can be considered as a specialcase of this type of MPD radiator, with the condition that N=0.

In a further embodiment, termed a single ended radial MPD radiator, aloop conductor has a plurality S of single-ended feeds which span aphase space of 2Nπ, where N is an integer, and each feed has a phaseshift of 2πN/S compared to each of the two adjacent feeds. An example ofsuch a single ended radial MPD radiator was fabricated and describedherein, in conjunction with FIG. 14.

Another embodiment involves a linear MPD radiator, in which a linearantenna structure is driven with differential feeds, where each feed isthe same phase. An example of such a linear MPD radiator is illustratedin FIG. 3.

Yet another embodiment involves a linear MPD radiator, in which a linearantenna structure is driven with single ended feeds, where each feed isthe same phase. Replacing the differential feeds of the exampleillustrated in FIG. 3 with single ended feeds is such an embodiment.

The phase shifts between the successive feeds in the linear embodimentsneed not be discreet levels, such as the 2πN/S shift that is required ina loop topology, but rather can be done by shifting by any real number Rradians from one feed to the adjacent feed. Such phase shifting isexpected to be useful for beam steering, in a similar way to phaseshifting in a conventional phased array.

In the MPD antennas used in the MPD radiators described in theembodiments given above, it is tacitly assumed that, for three or moreinput ports, the spacing between each pair of adjacent input ports isthe same spacing, and the frequency difference between the drivingsignals applied between any two adjacent input ports is the samefrequency difference. These criteria, which can be thought of asdefining a periodic structure which is driven with a series of drivingsignals differing by a constant offset in phase between successive inputsignals applied to successive input ports, are one convenient way todesign MPD antennas and MPD radiators according to principles of theinvention. However, there is a more general approach that can be used,of which the periodic design just described is a special case.

The more general design can be understood by first considering how theperiodic design functions, and then generalizing. In the periodicdesign, as will be explained in greater detail hereinbelow, there exista number of waves having a frequency determined by the common frequencyof the input signals that traverse the periodic structure. In thegeneral case, one can take the waves to be sinusoids, which are thebasis functions in a Fourier analysis. By calculating the phase of suchwaves at any location along either a linear MPD antenna or a loop MPDantenna, one can determine the relative phases that will be exhibited atany multiple number of locations along the antenna. Therefore, byapplying the principle of superposition, one could in principle drivesuch an antenna in an equivalent manner by selecting any multiple numberof locations along the antenna, which locations need not be arranged ina periodic spacing arrangement but rather can be situated at anyconvenient distances from each other (or at a series of distancesmeasured from one location considered to be the “starting location”)that one may select, determining the mutual phase relationships thatwould exist between each successive pair of such selected locations, andconstructing an equivalent antenna having the same number of input portsas the corresponding periodic antenna, but with input ports situated atthe selected locations, and operated by driving each such input portwith a signal having a phase difference from its adjacently appliedinput signal equal to the calculated phase difference between therespective locations of the adjacent input ports of the aperiodic array,which calculation is most conveniently performed by using the periodicmodel already discussed. See FIG. 13B Placing driving signal ports atselected locations, which may be non-regular points on the structure,can change the location of low impedance nodes or virtual shorts, butbecause the drives are often low impedance power sources, they can stillprovide drive power even if the impedance looking into the input portbecomes very low. This is the most general configuration that can beproduced for an MPD antenna in either linear or loop configuration, andis believed to be a technically feasible solution that provides asuitable MPD antenna and MPD radiator design. Clearly, if one were to“select” the multiple input port locations to be periodic and to supplythe corresponding input signals that are required, this general solutionbecomes one of the previously discussed periodic solutions.

One way to radiate power efficiently out of a lossy silicon substrate isto create a traveling wave current on a ring of approximately onewavelength in circumference, in a manner similar to a Distributed ActiveRadiator (DAR). This radiator is self-oscillating, because the reactiveelements of the antenna are also the reactive elements of theoscillator, and is not driven. The DAR radiates a harmonic frequency,and not the fundamental frequency. The DAR discussed in K. Sengupta andA. Hajimiri, “Distributed active radiation for THz signal generation,”in IEEE ISSCC Dig. Tech. Papers, February 2011, pp. 288-289, whichdescribes the integration of an oscillator, a frequency doubler and aradiator into one structure. See also K. Sengupta and A. Hajimiri,“Sub-THz beam-forming using near-field coupling of Distributed ActiveRadiator arrays,” Radio Frequency Integrated Circuits Symposium (RFIC),June 2011 and K. Sengupta and A. Hajimiri, “A 0.28 THz 4×4power-generation and beam-steering array,” International Solid StateCircuits Conference Digest (ISSCC), pp.256-258, February 2012.

Another type of integrated design is the Direct Antenna Modulation(“DAM”), discussed in A. Babakhani, D. B. Rutledge, and S. A. Hajimiri,“Transmitter Architectures Based on Near-Field Direct AntennaModulation,” Solid-State Circuits, IEEE Journal of, vol.43, no.12, pp.2674-2692, December 2008, which describes the integration of the antennaand modulation blocks into one structure. This structure is a singleport dipole on a chip with configurable passive reflectors placed aroundit. The power is only added from a single port, and is not driven bymultiple ports.

Unlike the DAR, our MPD radiating source is driven essentiallyunilaterally by the signal generation block at the fundamentalfrequency, eliminating the back coupling from the radiator itself.

The efficient active multi-drive radiator of the invention uses aplurality of drive points on a single radiating structure to create anefficient radiator. It utilizes the electical interdependence betweendrive points to allow electromagnetic situations not possible with asingle drive port or single drive point. It is possible to use aplurality of efficient active multi-drive radiators in a phased arrayconfiguration to further increase desired performance specifications.

Because the breakdown voltage of the transistors limit the maximumvoltage at the drain of the amplifier, in order to increase power, onecan only increase current. This implies that for high power devices, theoutput impedance preferably should be much below the load impedance thattradional antennas are designed to present. One option is to provide amatching network that transforms the low impedance of the transistoroutput to the higher impedance of the antenna. Alternatively, one candesign a radiator to present a low input impedance to the amplifiertransistor so as to eliminate the need for a lossy matching network. Theinput impedance of a radiating structure is determined by a combinationof the reactive elements such as inductances (lumped or distributed),and capacitance (lumped or distributed), lossy resistance and radiationresistance. For a wire-type radiator, similar to a traditional dipole orloop, one can gain additional intuition about the the input impedance bytreating or modeling the antenna as a transmission line of the samelength with extra loss due to the radiation impedance. The terminationof that line should either be open or short, in order to avoid dumpingpower into a terminal resistance which would decrease efficiency.

Using the transmission-line analogy, in order to have a low impedancewith open ends, the length from the amplifier to the open circuit shouldbe of the order of λ/4 (e.g., one-quarter wavelength), but due to theradiation impedance, the radiation resistance alone is 36.5 Ω. Evenwithout the loss resistance, that is a higher impedance than one wouldhope to achieve. In one particular standard CMOS 65 nm process, theinput impedance of one such stage is 10+10j. One additional issue isthat a λ/4 line is quite large, and one might prefer to have severalstages on a single chip to increase output power.

Alternatively, one can consider having a short at the end of the line.At first this does not look possible, as having a short would implyreturning the end of the line back to the amplifing transistor in somesort of a loop. However, a loop that is that small has very lowradiation efficiency, as the current around the loop is essentiallyconstant, and the opposing currents from opposite sides of the loop arevery close together. However, the use of a virtual short allows forseparation of the opposing currents and makes higher radiationefficiency levels possible. In one embodiment, in order to achieve thisvirtual short, differential drivers are placed at the corners of asquare as seen in FIG. 1. FIG. 1 is a schematic diagram of an activemulti-drive radiator according to principles of the invention.

By symmetry, the midpoint of each line will be a virtual short as eachend is being driven differentially. This will have the effect of makinga large loop with constant current around the entire loop, as long asthe the length of half of a side of the square (mr) is short enough thatthe current along it can be approximated as constant. By adjusting mr,the input impedance of each transistor stage can be adjusted. When mr=0,the impedance is 0. As mr increases, the imaginary part of the inputimpedance increases similarly to a shorted transmission line. At thesame time, both the loss resistance and the radiation resistance willincrease. Thus mr is set so that the input impedance matches the optimalload impedance of the amplifier stage, in this example, 10+10j. Becauseof the constant current on the loop, in the far field along the z axis(perpendicular to the plane of the antenna), opposing currents onopposite sides of the square will cancel out and it will not radiate inthat direction, but instead will exhibit end fire radiation in the planeof the antenna, and will result in an annular antenna pattern. This willtake advantage of the fact that on CMOS silicon, transistors can beplaced at any point of the structure at no additional cost, and thus itbecomes advantageous to drive the radiator from several points insteadof a single feed point. This design is advantageous in applicationswhere it is desired to radiate in the plane of the silicon chip. Alimitation is that such a design can cause issues with substratecoupling and additional interference with other circuits located on thechip.

In the embodiment shown in FIG. 1, differential driving amplifiers areplaced around the radiator and fed by input signals through transmissionlines along the input feed lines. DC power is provided by the Vdd feedline that connects to the radiator at the virtual short. By connectingat the virtual short, the impedance seen looking into the Vdd feed lineis no longer relevant as it will be in parallel to the virtual short,and thus a short will still be seen looking toward the virtual shortfrom the output amplifier stages.

FIG. 2 is a three dimensional plot of radiation intensity as a functionof direction for the embodiment of FIG. 1. As can be seen from the plotof directivity, this structure radiates along the XY plane, with verylow directivity along the Z axis.

The linear multi-port driven radiator allows for out of plane radiationand still achieves low input impedance. If one makes a structure similarto the square standing wave radiator shown in FIG. 1, but that iscompletely linear, the currents no longer cancel out in the z direction.This works acceptably for many of the stages in the middle, but breaksdown at the two ends where the virtual short no longer provides lowimpedance. Large blocks of metal are placed at these junctions toprovide as low of an impedance as possible. These end stages will bemuch more lossy than their counterparts toward the center of theradiating structure, but they will provide the appropriate current sinkallowing for all of the other virtual shorts in the center to occur.Because of this behavior, in order to maximize efficiency, it isdesireable to make as many stages as possible. One possible design wouldbe to put 8 differential stages in the radiator (having 16 drivingpoints), but it could be extended to include as many stages as arenecessary or as can be made available taking into consideration spaceand power constraints.

The linear multi-port driven radiator can be fed by an input dividersimilar to one used on a power-combining power amplifier (PA). Becausethe input feeds will be coming in perpendicular to the radiatingstructure, they will not interfere with the radiation very much. DCpower can be delivered by attaching a VDD connection to the virtualgrounds, and the DC ground can come in on the transmission line inputs.All of these lines can be perpendicular to the radiator currents.

Advantages provided by this structure include elimination of theinterconnect to an off chip antenna, and also elimination of the thepower combiner that would be required in a traditional PA to bring all 8differential stages together to 1 differential output.

FIG. 3 is a schematic diagram of a linear device, a constant currentdipole active radiator, according to principles of the inventiondeposited on a silicon substrate.

In one embodiment of the design shown in FIG. 3, a reflecting groundplane can be placed on the opposite side of the silicon substrate, todirect all of the energy up in one direction. By carefully selecting thedimensions of the substrate, a maximum amount of radiated power can bedirected in the positive Z axis. Similar to the square standing waveactive radiator described previously, the input signal is brought to theradiating elements through transmission lines. The lines then drivedifferential amplifying stages placed directly at the radiatingelements. This structure will create a standing wave, and mimics adipole that has more consistent current across it's line, but has theadvantages of being driven at multiple drive points, all having lowimpedances.

FIG. 4 is a plot of current density in the device of FIG. 3. Asanticipated, the structure has a maximum amplitude of current toward thecenter, and less current toward the edges where the concept of thevirtual short breaks down. In this embodiment, there are 8 pairs ofoutput differential stages, but more could be added to increase outputpower and efficiency.

FIG. 5 is a three dimensional plot of the radiation gain patternachieved by the device shown in FIG. 3 after tuning of the substrate.The high directivity of this radiator allows it to send more power to areceiver using the same input power, leading to an overall increase inefficiency.

FIG. 6 is a three dimensional plot of gain as a function of variationsin the x, y, and z dimensions of the device of FIG. 3. The substrate canbe tuned for maximum directivity by sweeping the x, y, and z dimensionsand finding the trends that occur. FIG. 6 presents one example plotwhere the Z dimension (Zsub) is kept constant and the x and y are swept.Tuning of the substrate's dimensions is advantageous to avoidsignificant loss to substrate modes.

FIG. 7 is a graph of gain as a function of substrate thickness (Zsub).The plot in FIG. 7 shows how the gain changes based upon substratethickness. The maxima occur when the substrate is M×wavelength/4 (e.g.,Mλ/4), where M is an odd integer, as the reflections off of the bottomground plane receive a 180° phase shift, and travel the distance of thethickness of the substrate twice before reaching the top of the chipagain with a complete 360° phase shift which adds coherently with theradiated waves leaving the radiating elements in the positive z axis.When M is even, they add out of phase and efficiency goes down. From themaximum to the minimum emission efficiency, this effect can have morethan 15 dB change in gain.

An important observation is that in order to have very low inputimpedances, the current between the radiator and the ground (virtual orreal) will be almost constant. If the currents all are in phase and comeback to the starting point to form a loop, they will cancel in the +Zdirection in the far field.

One approach to avoid this outcome is to not have the currents come backto the starting point as in the linear multi-port driven radiator. Analternative solution is to not drive all of the output stages in phase.To create symmetry one way of implementing this out of phase radiator isto mimic a traveling wave on a ring, as seen in FIG. 8. FIG. 8 is aschematic diagram of an embodiment of a differential radial multi-portdriven radiator with a loop topology. A central oscillator can be placedat the center of the radiator loop, and can send out input signalsthrough the ‘spokes’ to amplifier stages along the exterior.

If each input is driven differentially, so that each differential pairis driven with a phase addition compared to the previous pair in such away that the phase difference is 360° around the entire ring, a sort oftravelling wave is produced. With 2 driver stages, a standing wave isproduced, as there is no asymmetry to drive the wave either clockwise orcounter clockwise around the loop. This standing wave can be consideredas a degenerate travelling wave. With 4 stages driven at the phases 0°,90°, 180° and 270°, a traveling wave is formed. A center feed structurecan also be considered as seen in FIG. 8.

We now provide a brief analysis of the design issues using a 360° (2πradians) phase shift (or an integral multiple of 360°, or 2Nπ radianswhere N is an integer other than zero) around the ring. In order to havecontinuous phase shift with no jumps, the cumulative, or total, phaseshift must be N×360° as the same point on the ring must have the samephase. For any even integer N, the phase on the opposite side of thering will be in phase with the phase on the near side of the ring, andall currents will cancel each other out in the far field in the positivez axis. That is, the relative phase of the wave propagating around thering will be the same on opposite sides of a “diameter” of the loop. ForN=1 or other higher odd integer N, the currents on opposite sides of a“diameter” will not be exactly in phase, so such a design would providea far field signal. For odd integer N, a design that requires 16*Nspokes to achieve a 22.5° phase shift between drive points may becomecomplex to fabricate, and at present would be difficult because presentsemiconductor foundries generally allow angular relationships of notless than 45° for metal lines. Therefore, at present, a design havingN=1 is a preferred embodiment.

A 4 stage feed structure will allow for a centrally placed ringoscillator to drive the circuit, and send phase shifted input signalsdown the ‘spokes’ of the radiator. Because the spokes are perpendicularto the closest sections of the radiator at all times, they have littleeffect on the radiator. With 90° shifts however, the concept of avirtual ground in the center of the lines is lost, and in fact thetrailing amplifier will actually accept power rather than provide power.It is apparent that the phase shift must be more than 0° to induce atravelling wave, but less than 90° to allow all amplifier stages toprovide power. Using 8 spokes, the phase shift is reduced to 45° betweenadjacent spokes. This approaches the goal, but the asymmetry between theleading transistor and the trailing transistor in the differential pairis appreciable. Using 16 spokes and a 22.5° phase shift between adjacentspokes appears to be a good compromise between the asymmetry of theleading and lagging transistors, and the need for a phase shift toinduce a travelling wave.

FIG. 9 is a plot of the current density in the differential radialmulti-port driven radiator of FIG. 8 at 0° phase. As can be seen, thecurrents on opposite sides of the radiator are in phase.

FIG. 10 is a plot of the current density in the differential radialmulti-port driven radiator of FIG. 8 at 90° phase. The examination ofthis and other phase points show that there is indeed a traveling wavebeing produced around the loop structure.

FIG. 11 is a schematic diagram of a second embodiment of a differentialradial multi-port driven radiator in a loop topology. The embodiment ofFIG. 11 includes a ground plane and DC power/input signal feeds. Thisstructure could either have a ground plane on the bottom to facilitatefront-side radiation, or could leave the backside open and radiate inthat direction. For the following plot, backside radiation isconsidered.

FIG. 12 is a three dimensional plot of the radiation pattern emitted byan active multidrive radiator in a loop topology. The radiation patternof FIG. 12 shows a broad beam that is appropriate for putting into aphased array. Such an array of these devices would allow for beamsteering with the addition of phase shifters between loops. It has alsobeen observed that traveling, circularly polarized waves do not createnearly as much substrate loss as standing waves that are linearlypolarized. This effect can be used to increase the efficiency of such astructure.

These fundamental embodiments can be further improved through the use ofdigital and/or analog programming of the amplitudes and phases of theinput signals and/or power supplies. In such an embodiment, features ofthe radiation that can be programmed include steering the beam,adjusting the beam width, modifying the output power level, modifyingthe efficiency and adding a modulated signal on top of the fundamentalcarrier as well as other improvements to desired performancespecifications. These programmable controls can be implemented using ageneral purpose programmable computer operating under a set ofinstructions recorded on a machine readable medium, or alternatively canbe controlled by hardwired logic.

Another possible embodiment is to adapt the differential radial MPD intoa single ended version. The single ended radial MPD radiator uses anunbroken loop that is pumped by the driving circuitry at various pointsalong the loop single ended. The phases of each drive around the loopwill still be spaced substantially evenly in a similar manner to thedifferential version. The radial ground currents created by the activedrivers of the single ended radial MPD can also be designed to radiatecoherently with the signal current in the loop. This is accomplished bycreating ground ‘spokes’ that direct the ground currents radiallyperpendicular to the nearest point on the ring, resulting in radialstanding current waves along the spokes and a virtual ground at thecenter of the radiator.

FIG. 13A is a schematic block diagram of an embodiment of a single endedradial multi-port driven (MPD) radiating source having 8 drive spokes ina periodic structure.

FIG. 14 is a schematic diagram of the instantaneous current distributionon antenna signal and ground paths at 0° phase. Traveling wave currentsare shown as solid arrows, while standing wave currents are shown bydashed arrows. The peak traveling wave current in the ring leads thepeak injected current by about 45°, and thus the travelling signal waveon the ring and standing radial ground wave on the spokes are addingprimarily constructively in the far field. In order to create thetraveling wave on the ring, at least 3 drives are required, but forpractical design purposes a power of two (e.g., 2^(X), where X is aninteger greater than or equal to 2) is preferable for the number ofspokes. In the embodiment of FIG. 14, X=3. The ground spokes provideshielding for signal feed lines that connect the oscillator andamplifier core out to the ring by providing a closed path for the returncurrent. The spokes are extended out to a ground plane that is placed ata farther distance to the center to ensure that most of the RF groundcurrents go through the center of the radiator. These spoke extensionsalso allow for DC supply lines to be shielded from picking up any of theradiated signal.

The silicon substrate has a dielectric constant 11.7 times that of air,and thus most of the power that is radiated goes down into thesubstrate. While it is possible to radiate out of the backside of thechip this way, due to the practical thermal and packaging concerns it ispreferable to radiate from the top side by mounting the chip on aconductive backplane.

REDUCTION TO PRACTICE

An 8-spoke exemplary single ended radial MPD radiating source comprisingactive drive circuitry and a loop MPD antenna operating at 160 GHz wasdesigned and fabricated in a 130 nm SiGe BiCMOS process with two 3 μmcopper top metal layers. The total area available within the center ofthe radiator is small, and thus it is preferable to employ a poweroscillator to provide sufficient power directly. A single amplifyingstage is used next to amplify the signal and provide reverse isolationbetween the radiator and oscillator. The central oscillator is a 4-stagedifferential ring oscillator that provides eight phases 45° apart.

FIG. 15 is a schematic circuit diagram of an 8-phase ring oscillator andpower mixer, in which the bias circuitry is omitted for simplicity. Eachstage is a cascode stage for increased power and voltage swing, andemploys tuned metal capacitors for ac-coupling of the stages. Theresults of O. Momeni and E. Afshari, “High Power Terahertz andMillimeter-Wave Oscillator Design: A Systematic Approach,” IEEE J. ofSolid-State Circuits, vol.46, no.3, pp.583-597, March 2011 are used todetermine the interstage connections of the oscillator. Each of theeight oscillator phases is then fed to a cascode amplifying stage, whichprovides 6 dB gain and −7 dBm output power at 160 GHz each in simulationfor a total simulated output power of 2 dBm. FIG. 16 is a circuitdiagram of a power amplifier. The MPD antenna has a simulated radiationefficiency of 24%, and directivity of 8.8 dB, yielding a gain of 2.5dBi, and a maximum equivalent isotropic radiated power (EIRP) of 4.5dBm.

The chip was thinned to around 190 μm, mounted on a PCB, and attached toa 2-D stepper motor setup to measure the antenna pattern. The patternwas measured using a receiver comprising a 23.4 dB gain linearlypolarized horn antenna and a 10^(th) harmonic WR-6 mixer fed into aspectrum analyzer. The receiver was calibrated using a 160 GHz triplersource and an Erikson power meter. All measurements were taken with aseparation of 75 mm, or 40 at 160 GHz. The chip was rotated in the x-yplane and confirmed to have circular polarization. The radiator wasmeasured to have a maximum 4.6 dBm EIRP, at a frequency of 161.45 GHzwhile dissipating 384 mW, in close agreement with simulation.

The calibrated power spectrum observed at the receiver is depicted inFIG. 17. The radiation pattern was measured, and shows a total radiatedoutput power of −2 dBm. Two perpendicular slices of the radiationpattern measured by rotating the chip in the elevation and azimuthplanes are presented in FIG. 18A and FIG. 18B. FIG. 18A is a plot of thesimulated and measured antenna patterns in the elevation plane. FIG. 18Bis a plot of the simulated and measured antenna patterns in the azimuthplane.

FIG. 19 is an image of a die containing an embodiment of the singleended radial MPD radiating source that was fabricated and tested.

A Table that provides a comparison of integrated (on-chip) siliconradiators above 100 GHz is provided. To the best of the authors'knowledge, this work shows the highest reported on-chip radiated powerin silicon above 100 GHz. In the Table, the reference numbers [1], [2],[4], [5] and [6] represent the work described in the publications listedbelow. References [4], [5] and [6] describe single port antennastructures.

[1] K. Sengupta and A. Hajimiri, “Sub-THz beam-forming using near-fieldcoupling of Distributed Active Radiator arrays,” Radio FrequencyIntegrated Circuits Symposium (RFIC), June 2011;

[2] K. Sengupta and A. Hajimiri, “A 0.28 THz 4×4 power-generation andbeam-steering array,” International Solid State Circuits ConferenceDigest (ISSCC), pp. 256-258, February 2012.

[4] E. Laskin, et al., “170-GHz transceiver with on-chip antennas inSiGe technology,” Radio Frequency Integrated Circuits Symposium Digest(RFIC). pp. 637-640, June 2008;

[5] A. Tang, et al, “A 144 GHz 0.76 cm-resolution sub-carrier SAR phaseradar for 3D imaging in 65 nm CMOS,” International Solid State CircuitsConference Digest (ISSCC), pp.264-266, February 2012; and

[6] J. D. Park, et al., “A 0.38 THz fully integrated transceiverutilizing quadrature push-push circuitry,” Symp. on VLSI Circuits(VLSIC), pp.22-23, June 2011.

DEFINITIONS

Recording the results from an operation or data acquisition, such as forexample, recording results at a particular frequency or wavelength, isunderstood to mean and is defined herein as writing output data in anon-transitory manner to a storage element, to a machine-readablestorage medium, or to a storage device. Non-transitory machine-readablestorage media that can be used in the invention include electronic,magnetic and/or optical storage media, such as magnetic floppy disks andhard disks; a DVD drive, a CD drive that in some embodiments can employDVD disks, any of CD-ROM disks (i.e., read-only optical storage disks),CD-R disks (i.e., write-once, read-many optical storage disks), andCD-RW disks (i.e., rewriteable optical storage disks); and electronicstorage media, such as RAM, ROM, EPROM, Compact Flash cards, PCMCIAcards, or alternatively SD or SDIO memory; and the electronic components(e.g., floppy disk drive, DVD drive, CD/CD-R/CD-RW drive, or CompactFlash/PCMCIA/SD adapter) that accommodate and read from and/or write tothe storage media. Unless otherwise explicitly recited, any referenceherein to “record” or “recording” is understood to refer to anon-transitory record or a non-transitory recording.

As is known to those of skill in the machine-readable storage mediaarts, new media and formats for data storage are continually beingdevised, and any convenient, commercially available storage medium andcorresponding read/write device that may become available in the futureis likely to be appropriate for use, especially if it provides any of agreater storage capacity, a higher access speed, a smaller size, and alower cost per bit of stored information. Well known oldermachine-readable media are also available for use under certainconditions, such as punched paper tape or cards, magnetic recording ontape or wire, optical or magnetic reading of printed characters (e.g.,OCR and magnetically encoded symbols) and machine-readable symbols suchas one and two dimensional bar codes. Recording image data for later use(e.g., writing an image to memory or to digital memory) can be performedto enable the use of the recorded information as output, as data fordisplay to a user, or as data to be made available for later use. Suchdigital memory elements or chips can be standalone memory devices, orcan be incorporated within a device of interest. “Writing output data”or “writing an image to memory” is defined herein as including writingtransformed data to registers within a microcomputer.

“Microcomputer” is defined herein as synonymous with microprocessor,microcontroller, and digital signal processor (“DSP”). It is understoodthat memory used by the microcomputer, including for exampleinstructions for data processing coded as “firmware” can reside inmemory physically inside of a microcomputer chip or in memory externalto the microcomputer or in a combination of internal and externalmemory. Similarly, analog signals can be digitized by a standaloneanalog to digital converter (“ADC”) or one or more ADCs or multiplexedADC channels can reside within a microcomputer package. It is alsounderstood that field programmable array (“FPGA”) chips or applicationspecific integrated circuits (“ASIC”) chips can perform microcomputerfunctions, either in hardware logic, software emulation of amicrocomputer, or by a combination of the two. Apparatus having any ofthe inventive features described herein can operate entirely on onemicrocomputer or can include more than one microcomputer.

General purpose programmable computers useful for controllinginstrumentation, recording signals and analyzing signals or dataaccording to the present description can be any of a personal computer(PC), a microprocessor based computer, a portable computer, or othertype of processing device. The general purpose programmable computertypically comprises a central processing unit, a storage or memory unitthat can record and read information and programs using machine-readablestorage media, a communication terminal such as a wired communicationdevice or a wireless communication device, an output device such as adisplay terminal, and an input device such as a keyboard. The displayterminal can be a touch screen display, in which case it can function asboth a display device and an input device. Different and/or additionalinput devices can be present such as a pointing device, such as a mouseor a joystick, and different or additional output devices can be presentsuch as an enunciator, for example a speaker, a second display, or aprinter. The computer can run any one of a variety of operating systems,such as for example, any one of several versions of Windows, or ofMacOS, or of UNIX, or of Linux. Computational results obtained in theoperation of the general purpose computer can be stored for later use,and/or can be displayed to a user. At the very least, eachmicroprocessor-based general purpose computer has registers that storethe results of each computational step within the microprocessor, whichresults are then commonly stored in cache memory for later use, so thatthe result can be displayed, recorded to a non-volatile memory, or usedin further data processing or analysis.

Many functions of electrical and electronic apparatus can be implementedin hardware (for example, hard-wired logic), in software (for example,logic encoded in a program operating on a general purpose processor),and in firmware (for example, logic encoded in a non-volatile memorythat is invoked for operation on a processor as required). The presentinvention contemplates the substitution of one implementation ofhardware, firmware and software for another implementation of theequivalent functionality using a different one of hardware, firmware andsoftware. To the extent that an implementation can be representedmathematically by a transfer function, that is, a specified response isgenerated at an output terminal for a specific excitation applied to aninput terminal of a “black box” exhibiting the transfer function, anyimplementation of the transfer function, including any combination ofhardware, firmware and software implementations of portions or segmentsof the transfer function, is contemplated herein, so long as at leastsome of the implementation is performed in hardware.

THEORETICAL DISCUSSION

Although the theoretical description given herein is thought to becorrect, the operation of the devices described and claimed herein doesnot depend upon the accuracy or validity of the theoretical description.That is, later theoretical developments that may explain the observedresults on a basis different from the theory presented herein will notdetract from the inventions described herein.

Any patent, patent application, or publication identified in thespecification is hereby incorporated by reference herein in itsentirety. Any material, or portion thereof, that is said to beincorporated by reference herein, but which conflicts with existingdefinitions, statements, or other disclosure material explicitly setforth herein is only incorporated to the extent that no conflict arisesbetween that incorporated material and the present disclosure material.In the event of a conflict, the conflict is to be resolved in favor ofthe present disclosure as the preferred disclosure.

While the present invention has been particularly shown and describedwith reference to the preferred mode as illustrated in the drawing, itwill be understood by one skilled in the art that various changes indetail may be affected therein without departing from the spirit andscope of the invention as defined by the claims.

What is claimed is:
 1. A multi-port driven antenna, comprising: anantenna structure having a length L, said antenna structure comprising aconductor and configured to radiate electromagnetic radiation, saidradiator structure having at least one ground contact point and aplurality S of input ports, where S is a positive integer greater thanor equal to 2, each of said plurality S of input ports having arespective electrical connection to said antenna at a respectiveselected location along the antenna length L; and a respective signalinput terminal of each of said plurality S of input ports, each signalinput terminal configured to receive a respective input signal having apredetermined phase relationship with respect to another input signalapplied to an adjacent signal input terminal, said predetermined phaserelationship dependent on said location of said respective electricalconnection to said antenna, said respective signal input terminalconfigured to apply said received respective signal to said antennastructure at said respective selected location of said input port. 2.The multi-port driven antenna of claim 1, further comprising: a sourceof input signals, said source configured to provide to each of saidrespective signal input terminal of each of said plurality S of inputports said respective input signal having a predetermined phaserelationship with respect to another input signal applied an adjacentsignal input terminal, and configured to provide a ground signal at eachof said at least one ground contact point; said multi-port drivenantenna and said source of input signals when active defining amultiport-driven radiator.
 3. The multi-port driven antenna of claim 2,wherein said source of input signals includes an amplifier configured toamplify at least one of said respective input signals.
 4. The multi-portdriven antenna of claim 1, wherein said antenna structure having alength L is a loop structure.
 5. The multi-port driven antenna of claim4, wherein each of said plurality S of input ports has a respectiveelectrical connection separated by a length L/S from a location of anadjacent input port.
 6. The multi-port driven antenna of claim 2,wherein said signal source is a multi-phase oscillator.
 7. Themulti-port driven antenna of claim 2, wherein said multi-phaseoscillator is configured to provide 2^(X) phases, where X is an integergreater than or equal to
 2. 8. The multi-port driven antenna of claim 1,wherein said antenna is configured to radiate millimeter waveelectromagnetic radiation.
 9. The multi-port driven antenna of claim 1fabricated on a semiconductor wafer.
 10. The multi-port driven antennaof claim 1, further comprising at least one ground plane adjacent saidloop antenna structure.
 11. The multi-port driven antenna of claim 1,further comprising a controller configured to control an amplitude and aphase of each of said respective input signals.
 12. The multi-portdriven antenna of claim 1, further comprising a controller configured tocontrol a power supply.
 13. The multi-port driven antenna of claim 1,configured as one of a plurality of multi-port driven antennas in aphased array configuration.
 14. The multi-port driven antenna of claim1, wherein said antenna structure having a length L is a linearstructure.
 15. A method of generating electromagnetic radiation,comprising the steps of: providing an antenna comprising: an antennastructure having a length L, said antenna structure comprising aconductor and configured to radiate electromagnetic radiation, saidradiator structure having at least one ground contact point and aplurality S of input ports, where S is a positive integer greater thanor equal to 2, each of said plurality S of input ports having arespective electrical connection to said antenna at a respectiveselected location along the antenna length L; and a respective signalinput terminal of each of said plurality S of input ports, each signalinput terminal configured to receive a respective input signal having apredetermined phase relationship with respect to another input signalapplied an adjacent signal input terminal, said predetermined phaserelationship dependent on said location of said respective electricalconnection to said antenna, said respective signal input terminalconfigured to apply said received respective signal to said antennastructure at said respective selected location of said input port;applying each of a plurality S of input signals each having a frequencyω to a respective signal input terminal of each of said plurality S ofinput ports; and observing an electromagnetic radiation output signal ata frequency ω.
 16. The method of generating electromagnetic radiation ofclaim 15, wherein said integer S is three or larger.
 17. The method ofgenerating electromagnetic radiation of claim 15, wherein said integer Sis a power of
 2. 18. The method of generating electromagnetic radiationof claim 15, wherein said integer S is
 8. 19. The method of generatingelectromagnetic radiation of claim 15, wherein said electromagneticradiation is millimeter wave electromagnetic radiation.